I'm sure I was never told about carb heat when pulling power back to idle to practice stalls.
So, without being told anything different, I would naturally have pulled the carb heat as well when told to reduce power to idle.
And, being a 152, when applying power to recover I would have put carb heat back to cold in the same movement, as you say, but personally I'm pretty sure I use the thumb rather than the palm.
I have no recollection of an instructor telling me I was doing this wrong so they must have thought I was doing it right.